My GORGEOUS Agfa Isolette - Depth of field v. Depth of focus ?

So I bought this incredibly beautiful Agfa folder from a guy who

fixes them up (Jurgen Kreckel, certo6). Check it out:

 

http://www.inqs.com/pics/agfa4.jpg

 

My question - the camera has an uncoupled rangefinder, and I am

trying to find out what will be in or out of focus at a designated

lens opening. I guess that's two questions:

 

1. What is the difference between "depth of field" and "depth of

focus" ?

 

2. How do I determine what will be in focus at a given lens opening ?

 

Thank you in advance for the help.

 

fR3d

When you stop down a lens, the depth of the field of focus increases both behind and in front of the lens. In front, itis called depth-of-field, and behind, it is called depth-of-focus. The DOF of all similar focal length lenses is approximately the same, so look up the DOF of your lens on a DOF chart.

Lenses of that era usually have DOF markings on the focusing scale, so determine the subject distance with the rangefinder, and you can go by the markings on the lens. To be on the safe side, particularly if you might want to make a big enlargement, you might refer to the DOF markings one or two stops wider than the actual lens aperture (so if the exposure calls for f:11, you might use the markings for f:8 or f:5.6).

 

If there are no DOF markings on the lens, there are a few DOF calculators on the net. The one I like is "f/calc", which is a shareware program that runs in Windows and does various photographic calculations. You can make your own scale and tape it to the back of the camera for reference.

Depth of field occurs out in the subject (hence 'field'), depth of focus occurs at the film-plane. The two are related but depth of field is the one we are most commonly interested in.

Depth of field refers to the range of "acceptably sharp" focus in front of and behind the object you have focused on. Smaller lens openings (larger numbers) give more depth of field. I have read in a Kodak publication that one third of the depth of field is in front of the exact object of focus, two thirds is behind that object. There is a fellow named Mecklinger (Merklinger?) who has written extensivly on this subject, much of his work is available on the web. Note that "acceptably sharp" depends depends on several factors one of which is the size of "circles of confusion" on the film.

Depth of focus is a relativley narrow range of distance in which the image formed by the lens is focused on the film. Cameras have pressure plates to keep the film flat because depth of focus is never very deep. Enjoy your new camera!

Freddie �

 

Like you, I bought an Isolette from Jurgen. Also like you, I've been dealing with the lack of depth-of-field markings on the lens. I have downloaded the DOF programs, I've customized the DOF spreadsheets. � And I find I don't use either.

 

As another responder noted, you should check into the writings of Harold M. Merklinger. He is the author of a couple of books, and wrote a series of articles on focusing for Shutterbug. These articles are available on the web, and I have applied the concepts in them *very* successfully with my Isolette.

 

A good place to start reading is at http://home.fox.nstn.ca/~hmmerk/DOFR.html. A Google search for 'Merklinger' will also turn up other references.

 

Good luck with your Isolette. I took my Isolette with me on a recent business trip to Europe, and had an opportunity to do some reasonably serious photography. I printed up my first 11x14s the other day from the trip and was extremely pleased with the quality. As long as I stayed off of F22 the pictures seemed to be equivalent in quality to those taken by my much more expensive 645 SLR outfit.

 

� Bill

bill -- you shouldn't wish merklinger on anybody!! he's abstruse and occasionally just plain wrong!! interesting stuff nonetheless (although his "focusing the view camera" stuff reflects little practical experience). asembling a DOF table for your lens is a good idea -- most linhof's come with one attached to the inside of the hood/GG cover that gives info for pop focal lengths. A WORD OF WARNING ABOUT MOST DOF tables: remember, in the main, these tables reflect some technicians idea about what constitutes an acceptibly small circle of confusion circa 1950!!! (when most of these tables were drawn up). progress in films/paper/lenses has created a situation where these tables are too optimistic at the margins. today, many people assume that you must stop down a least one step beyond what is recommended by a lens engraving or a table. REMEMBER -- THERE IS ONLY ONE SINGLE SHARP PLANE OF FOCUS. EVERYTHING IN FRONT OF OR BEHIND THE PLANE WILL BE OUT OF FOCUS TO A DEGREE. give yourself a nice margin of error and you will lead a happier and more socially useful life.

That is a beauty of a camera! I also use f/Calc as well. One nice aspect of this application is that it allows you to set the size of the circle of confusion (although I have never saw the need) -- which allows you to decide what is or is not acceptable.

I know I'm a day late and a buck and half short on this thread, but for the benefit of any future web surfer let me add the following

 

Even at f/8 or f/11, try to be as precise as possible in setting the distance to the subject using the distance setting on the lens. With regards to the hyperfocal scale, it really is, as described in an earlier response, a zone of soft focus, circa 1950 appropriate for amateur photograpy.

 

Besides impatience, there are a couple of things working against the modern user of an old medium format folder.

 

First, the depth of field as it is usually called, is not as forgiving on a 80mm lens as it is let's say on a Rollei 35 with a 40mm lens. On a 6x9 medium format, which uses a 105mm lens there is even less of a margin of error. As with the Rollei 35, most folders used guessamatic focusing. So, 12 ft can easily seem like 10 ft when guess-timating.

 

Now, throw in camera shake. I often find that I need to use a shutter speed of 1/50th or slower with ASA/ISO 100 film. This can happen easily even on a sunny day when using a yellow number two or a medium red filter. Hand-held photography 1/50th of second and an 80mm focal length is an iffy proposition with regards to shake. With a 105mm focal length any speed below a 1/100th second is subject to slow speed blur.

 

One work around if you wish to capture the both the subject and a distant background in proper focus is to step back a good bit capture more of the frame than you need, then crop the margins of the frame in the darkroom.

 

If one finds the percentage of guestimation focusing errors unacceptable, then buy a rangefinder attachment. That flash shoe on top of a bellows camera is really an attachment clip. The percentage of focusing errors go way down, when a rangefinder is used. I use a Russian made BLIK. Voigtlander, Ideal and Agfa are some other clip-on rangefinders that work well.

 

Last, but not least, use a tripod or a stout table pod to prevent camera shake. I hate to say it, but I do take better exposures with a tripod and a cable release than I do in the hand-held mode. Just be sure to hold down the base of any table pod to prevent the camera from tipping over accidentally.

 

One can have a lot of fun shooting with an old medium format folder. It can lead to another addictive habit, printing in your own darkroom.

I think a tripod defeats the purpose of using a medium format folder in the first place - high

quality images produced by a very portable camera. If you are going to lug a tripod around

(which I frequently do with my Nikon system with 5 lenses, filters, polarizers, cable release,

etc.) you might as well carry a more heavy duty, all-purpose camera.